The present invention relates generally to heat exchange apparatus and specifically to an element basket for a rotary regenerative heat exchange apparatus including means for retaining element plates within the basket while permitting relative movement between the plates thus preventing premature breakage of the element plates.
In rotary regenerative heat exchange apparatus, a mass of heat absorbent material commonly comprised of element plates is first positioned in a hot gas passageway to absorb heat from a stream of hot gases passing therethrough. As the heat absorbent material becomes heated by the hot gases, it is slowly moved into a second passageway where the heated plates transmit their absorbed heat to cooler air passing therethrough.
The apparatus of a rotary regenerative heat exchanger is commonly comprised of a cylindrical drum packed with heat absorbent plates, the rotor then slowly rotated about its axis to permit alternate contact with hot gas and cooler air. As the plates are contacted by the flow of air and gas, they corrode and erode until they occupy less space in the basket, thus becoming less tightly packed and becoming subject to vibration and ultimate breakage by the aerodynamic forces of the air and gas flowing through the rotor.
Severe vibration often results in premature breakage of the element plates so that the heat exchanger quickly loses its effectiveness. Although the heat absorbent plates are commonly contained in sector-shaped baskets that may be individually repaired or replaced as required, the operation of replacement usually requires that the heat exchanger be completely shut down and removed from service until repair is complete.
Another cause of plate deterioration and breakage is the application of concentrated stresses to points formed by sharply bending or cutting the plates to conform to their physical relationship with other plates or retaining bars within the basket.
Various arrangements have been developed to preclude the shifting of plates and thus prolong their effectiveness. One highly effective construction is seen in U.S. Pat. No. 3,314,472 where the heat absorbent plates are spring loaded to preclude their lateral movement or vibration. Another arrangement shown in U.S. Pat. No. 3,379,240 discloses a method of actually bending the individual element plates to effect a spring action which maintains the plates in a permanently tight relationship.
In U.S. Pat. No. 4,345,640 restraining bars are tightly recessed into ends of a series of element plates, the bars then being affixed to opposite walls of a basket so as to restrain the individual plates both endwise and transversely. To effect a complete restraint, the element plates are provided squarecornered recesses, the edges of the recesses in said plates tightly contacting the edges of the restraining bars. When the plates are subjected to the action of the moving air and gas, all vibration is at first precluded by the restraining bars. As the element plates deteriorate by prolonged exposure to the corrosive and erosive effects of the gas and air, they gradually occupy less space in the basket while the recesses in the plates gradually become larger. Thus, the plates loosen in the basket and begin to vibrate increasingly which may lead to cracking under stress at their square-cornered recesses and eventually result in the plates breaking apart and failing completely.
Although breakage of the element plates is caused primarily by vibrations generated by the flowing air and gas and the corrosiveness of the gas, it is hastened by distortion of the restraining bars tightly fitting into the recesses of the plates. Inasmuch as the bars have no margin of movement within the tightly fitting recesses of the plates, expansion and warping of the bars causes additional stress to be placed upon the element plates at the sharp corners of said recesses. Thus, cracking soon occurs and complete failure of the individual plates follows.